The present invention provides a seat weight measuring apparatus and supporting structure that can be installed in a vehicle without changing the height of the existing seat frame. This is done by shifting the center line of the sensor unit 2 from the center line of the seat frame 34/40/44 to take advantage of a space for the insertion of the sensor on the side of the frame. Accordingly, the seat height does not need to be raised by the thickness of the sensor unit 2 as required in the conventional seat weight measuring apparatus. Depending on where space is available underneath the seat, the sensor units may also be positioned perpendicular to the seat rail, in a xe2x80x9cYxe2x80x9d shape, or in a xe2x80x9cTxe2x80x9d shape.